Fifty‐seven of 800 human temporal bones were found to have eosinophilic perilymph precipitates. The most common etiological factor was blockage of the internal auditory canal (20 cases). Acute bacterial labyrinthitis (nine cases) and subarachnoid hemorrhage (five cases) were also associated with perilymph precipitates. Small amounts of precipitate were also observed in 20 of 110 temporal bones without evidence of ear pathology. Experimental introduction of serum proteins into the cat's perilymphatic space confirms that eosinophilic perilymph precipitates may represent increased quantities of protein in the perilymphatic spaces; however, no correlation could be made between the quantity of precipitate observed and the concentration of the protein in the perilymph. The finding of increased perilymph protein above 1,000 mg/100 ml during a diagnostic inner ear tap (labyrinthotomy) is good evidence for the presence of an acoustic neurinoma. An associated peripheral VIIth never paralysis should alert the clinician to the possibility of a metastatic carcinoma of the internal auditory canal.
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